Sources and transregional transport process of air pollutant in northern suburbs of Nanjing

Abstract:Based on the national air quality index(AQI),the ground-based PM2.5 data,the global assimilation system GDAS data and FNL reanalysis meteorological data,this paper studies the variation characteristics of air quality,environmental transport conditions and pollutant sources in the northern suburbs of Nanjing in the winter of 2015/2016.Results indicate that,represented by AQI,there are three typical pollutant transregional transport routes for winter pollution in Jianghuai area,and they are the northwest,north and southwest routes.The northwest route usually occurs at the time when the Mongolian high is strong and locates at the climatological position.At the same time,there is cold advection over the northern suburbs of Nanjing,which is not conducive to pollutant diffusion.The north route corresponds to weak Mongolian high and weak high near Northeast China.The northerly airflow brings pollutants to the northern suburbs of Nanjing.If it crosses the ocean,the pollutions will be reduced.The southwest route corresponds to the anticyclonic circulation center in the boundary layer in the northern suburbs of Nanjing,and the sinking airflow is very unfavorable for pollutant diffusion.The potential sources of pollution in the northern suburbs of Nanjing are mainly located in southern Hebei,western Shandong,southern Henan,eastern Anhui and western Hubei.Hebei Province is a crucial pollution source area,and the pollutants in southern Hebei and western Shandong are transported to the northern suburbs of Nanjing through the north route.Therefore,although the north route has less pollution probability than the other two routes,it is an important route to form severe pollution in the northern suburbs of Nanjing.Besides,pollutants in southern Henan are transported through the northwest route,and pollutants in Anhui and Hubei are transported through the southwest route.Quantitative analysis shows that the advection transport is an important cause of serious pollution in the northern suburbs of Nanjing.The contribution of near-surface wind speed to AQI advection is more than 70% or even 85%.